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[Xen-devel] Re: pv_ops & gntdev?



Gerd Hoffmann wrote:
Unmapping the grants when the kernel is about to zap the page range.
I think it could be easier because I don't have to link the low-level
paravirt code with the gntdev driver then.  Also I can easily batch
unmaps.  And there is a performance hit for the extra checks only for
processes which actually use grants.

Would the unmap operation on the vma be enough to do that? Hm, I guess vm_operations_struct needs something that gets called before the zap rather than after (->close).

The (unclean) exit case might be tricky though.  Could be the kernel
tries to unpin before zapping all mappings, so we don't trap into xen
all the time.

Yes, the unpin needs to make sure it clears out all the grant refs, because you just can't unpin otherwise.

The alternative is to hook into the fault handler so that a fault-n-emulate operation on the pagetable which fails because of the grant reference can be fixed up at that point. But that might be even more intrusive.

   J

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